The objective of the study was to quantify differences in nutritive value, over four seasons, of native grasses such as <i>Bouteloua curtipendula, Bouteloua trifida, Brachiaria fasciculata, Chloris ciliata, Digitaria insularis, Leptochloa filiformis, Panicum hallii, Panicum obtusum, Paspalum unispicatum, Setaria grisebachii, Setaria macrostachya, Tridens eragrostoides, Tridens muticu</i>s and naturalized <i>chrus ciliaris</i> and <i>Rhynchelytrum repens</i> that are used as forages for grazing beef cattle. <i>Cenchrus ciliaris</i> was included as a reference grass of good nutritional quality. Plants were collected in autumn 2001 and in winter, spring and summer 2002. The nutritive value was assessed in terms of nutrient content, effective rumen degradable dry matter (EDDM), metabolizable energy (ME) and metabolizable protein (MP). Most grasses had crude protein (CP) content comparable to the reference <i>C. ciliaris</i> grass (grand mean = 120 g/kg) and some of them had a higher content (140 g/kg). Cell wall (NDF) and lignin contents were lower in <i>C. ciliaris</i> (650 g/kg, 30, respectively) than in the other grasses (mean = 700 g/kg, 60, respectively). All grasses had less EDDM (mean = 420 g/kg) than <i>C. ciliaris</i> (470 g/kg). All grasses had the ME content (mean = 5.6 MJ/kg DM) that was lower for maintenance requirements of growing beef cattle. Conversely, mean MP values (67 g/kg DM) were sufficient. Lower content of P (annual mean = 120 g/kg DM), Na (0.3) and Cu (40 mg/kg DM) was detected in all grasses to meet the requirements of growing cattle. All grasses, in all seasons, had sufficient CP and MP content to meet the maintenance requirements of growing beef cattle. Higher levels of EDDM occurred in summer and autumn. Because of their good nutritional quality, grasses such as <i>B. fasciculata, C. ciliata, P. hallii, P. obtusum, S. grisebachii, S. macrostachy</i> and <i>T. eragrostoides</i> can be considered as good forages for ruminants.
